This invention relates to a system for displaying a trendgraph representing time-serially data collected, and more particularly to a trendgraph display system capable of enlarging or reducing trendgraphs.
In the prior art, the monitoring of various plants and the utilities such as fife warning networks in office buildings, water supplies and tunnel equipment has involved data collected from the monitoring area at fixed intervals being rendered as a trend graph. A trend graph shows the trends of the monitored phenomena over time so that, for example, if a fault occurs in the equipment being monitored, it is possible to obtain information about the cause of this fault from the trend graph and greater detail can be obtained by enlarging the trend graph. A trend graph scale alteration device controls the display of a trend graph.
In conventional trend graph scale alteration devices, as shown in FIG. 1, a trend graph is displayed in a display area 11 of a CRT screen at monitoring periods set by the operator's key-board. A movable cursor 12 displays a cursorline 12A on axis X, which is the time axis, in display area 11 of the trend graph. This movable cursor 12 is moved along axis X by the cursor movement keys. After the cursor 12 is moved, the graph information of part A at the intersection of the trend graph and the cursorline 12A of cursor 12 is displayed in a data display close to display area 11. If there is an input specifying an enlargement rate, the trend graph is displayed in enlarged form, with median line L1 at its center, in display area 11, as shown in FIG.2.
However, in such conventional trend graph scale alteration devices, since cursor 12 is moved manually using the cursor moving keys, the speed at which the cursor can be moved is limited and the time taken to move the cursor significantly inhibits improvement of operating efficiency. Moreover, when the trend graph is enlarged, the position of the cursor 12 is reset to a corner in display area 11 and the graph information displayed in the data display area is deleted.
Also as the trend graph is enlarged with median line L1 of axis Y at its centre, the necessary part of the graph is enlarged vertically and it may be impossible to inspect the adjoining sections of the graph or to display this within display area 11. When, as a result of the enlargement, the desired area cannot be displayed in display area 11, the display window must be scrolled along axis Y using the screen scroll key and cursor 12 is moved to this part, which is an extremely complex operation for the operator to perform.
Thus, conventional trend graph scale alteration devices require considerable time for cursor movement. And,when the trend graph is enlarged, the operations to render the required part of the trend graph susceptible to monitoring are complex. They thus have poor operating characteristics.